Don't crash on start up if macOS system font encoding is unknown

If the encoding is not recognized (which is the case at least for the
encoding used for Persian/Farsi), wxLocale::GetSystemEncoding() returns
wxFONTENCODING_DEFAULT and wxFont::SetDefaultEncoding() must not be
called in this case, as it asserts and, due to a separate bug, crashes
as the GUI is not fully initialized yet when wxApp::Initialize() is
executing.

See #25561.

(cherry picked from commit 5de590ffaf)

docs/changes.txt

@@ -272,6 +272,7 @@ wxMSW
 
 wxOSX:
 
+- Fix crash on startup when using Farsi as system language (#25561).
 - Do not activate "Close" button on Cmd-C (nobugshere, #25346).
 
 

src/osx/carbon/app.cpp

@@ -306,7 +306,12 @@ bool wxApp::Initialize(int& argc, wxChar **argv)
         return false;
 
 #if wxUSE_INTL
-    wxFont::SetDefaultEncoding(wxLocale::GetSystemEncoding());
+    // Check if we recognize the system encoding. Note that we must not call
+    // SetDefaultEncoding() if we don't, as indicated by wxFONTENCODING_DEFAULT
+    // being returned, as SetDefaultEncoding() would assert in this case.
+    const wxFontEncoding defaultEncoding = wxLocale::GetSystemEncoding();
+    if ( defaultEncoding != wxFONTENCODING_DEFAULT )
+        wxFont::SetDefaultEncoding(defaultEncoding);
 #endif
 
     // these might be the startup dirs, set them to the 'usual' dir containing the app bundle